I have gone through numerous previous posts and cannot find the answer to this. Please forgive me if I overlooked it.

QUESTION: How much power will a 1/3 hp or a 1/2 hp submerged well pump running at 70% capacity use? I cannot apply the figures I get from Grundfos/Franklin Motors/F&W for my situation. I am confident from reading previous posts that there are folks in this forum that are well versed in this.

BACKGROUND: I am building my home and plan to install a Climatemaster Model 049 - 4 ton geothermal heat pump. I am trying to determine which pump (open or closed loop) will be more economical for the heat sink since the water temperature and power consumption of the chosen pump clearly impacts the overall system EER/COP.

I have an abundance of good water at a depth of 50-55 feet here in NW Florida at year-round water temp of 68-69 degrees. If I utilize a horizontal loop 6' deep, my water temp will vary from the well water temp by approx 10 degrees. This does not take into account ground heat saturation during the long summer cooling load here in Florida which will further lower the efficiency of the closed loop. Will the increased EER/COP values at the more attractive well water temps be worth the added power consumption of the well?

Since I am already installing an irrigation well, the cost of installing an additional well for the water source is more competitive than installing a ground loop. I plan to use the irrigation well as the injection well to minimize the possibility of fouling the screens with the small amount of iron present (assuming air gets into system). I have been told by drillers in the area that pulling large amounts of water at a high rate of flow back out of the injection well should eliminate\reduce clogging of the injection well screens.

I am leaning toward the open system, but do not want the cost of running a well pump to make it more expensive. I am convinced we are on the precipice of vastly increasing utility costs and plan to live in this house for the rest of my life. What sayest thou?

One last question - Ideally, I want a 1/3 hp pump because of the low head. I cannot find a decent brand in a third horse. They have been discontinued. I am forced to buy a 1/2 horse, either Grundfos, Gould or F & W. Will the 1/2 hp pump use much more power than the 1/3 hp doing the same amount of work?

Okay, I lied. Second question comes to mind - In your opinion, which of the three is the best to go with, and are any to be avoided?

>Okay, I lied. Second question comes to mind - In your opinion, which of the three is the best to go with, and are any to be avoided?

In my opinion, you should run open loop first and use the savings to put in a more efficient drilled closed loop system. This is what I am planing.

The costs of "caseless" vertical wells should come down as drillers get used to drilling only until it gets difficult.

Drillers also need to change there rigs so that they can quickly change the angle they drill at so that you can drill at an angle to cover more area while reducing the size of the trench where the pipes are connected.

I've been thinking of building a rig that can drill 50 feet using 1-1/4 pipe and then pushing a pair of 1/2 pipe down each well before filling it with sand and pulling the 1-1/4 pipe back out.

Edit: oh. I think you are asking about which brand of pump to get, not which option to go with.

The VFD for your system isn't applied in the manner that is used for constant-pressure systems described on this board.

Most of the problems arise out of trying to make inexpensive constant-pressure control systems with inexpensive pressure transducers or pressure switches. The systems tend to cycle and hunt while they respond to varying demands of the system. You don't have that kind of system.

The inverter will not involve varying control, pressure transducers, or cycling the pump on and off to meet varying demand. It will simply convert the 240 VAC single phase input power at 60 Hz to 240 Volt 3-phase power to a frequency somewhere between 50 and 60 Hz to provide the pressure you need for the heat exchanger. You will dial the speed/pressure/flow that you need and leave it there.

Because the pump delivers more pressure and flow than you need you will never need to operate it above the rated speed, so you can use a standard pump with a VFD rated 3-phase motor of the specified horsepower. I know that Goulds sells pumps with such motors.

VFDs are used in many applications where saving energy is an important part of the control system. They are used because they save energy. There is some conversion loss but the net effect is to save energy. There is not standby loss because the VFD will not be powered when the system is off.

If you can match the pump to the system without a VFD that is the most efficient way to go.

If your system can accept higher flow then the extra pumping power will probably be balanced by reduced compressor power.

If you have to throttle the pump significantly then you can save energy with a VFD.